Generally, this recovery is effected by remelting the metallic scrap with the substantial elimination of the surface zinc by smelting the metallic scrap in a blast furnace or in an electric arc furnace. However, such smelting cannot be done except in very limited quantity and is far from being able to handle the existing stocks of such metallic scrap, which are sharply increasing, especially as sheet steel is used which is galvanized on one or both surfaces for the production of automotive vehicles. Given this impossibility of treating such quantities of galvanized sheet in a blast furnace or electric arc furnace, it has been studied whether it would be possible to use conventional foundry techniques, namely a cupola or an induction furnace.
As to a cupola, it has been determined that the latter even though operated with hot air can hardly receive a charge consisting of more than 25% of galvanized sheet steel. Beyond that, there is an instability of operation of the apparatus and a problem of adaptation of the filtration means ordinarily provided for the cupolas for treatment of fumes loaded with zinc vapor. As to induction furnaces, experience has shown an impregnation of the refractory of the crucible by zinc vapors which condense thereon and thus lead to short circuits of the windings of the inductors and, moreover, a certain quantity of zinc dissolves in the melt which even if it does not lead to a deterioration of the metallic properties of the melt, provokes substantial and very serious pollution of the workplace of the foundry during transfer of the melt in a ladle, in the course of which zinc vapors escape which are particularly injurious to the health of personnel in the vicinity.